Structures and methods for high speed interconnection in photonic systems

ABSTRACT

Structures and methods for high speed interconnection in photonic systems are described herein. In one embodiment, a photonic device is disclosed. The photonic device includes: a substrate; a plurality of metal layers on the substrate; a photonic material layer comprising graphene over the plurality of metal layers; and an optical routing layer comprising a waveguide on the photonic material layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/007,743, filed Aug. 31, 2020, which is incorporated by referenceherein in its entirety.

BACKGROUND

Photonic integrated circuits (PICs) integrate various electroniccomponents, e.g. serializer/deserializer (SerDes) circuits,transceivers, clocking circuitry, and/or control circuitry. With thelong range SerDes reaching its speed limit, on-chip or in-packageoptical input/output (I/O) circuits are taken as the most promisingcandidates to further boost the speed.

Conventionally, silicon photonics based on a silicon on insulator (SOI)platform or substrate are used to achieve high speed optical I/O, whichinduces a relatively thick crystal silicon layer and a thick oxidelayer. In addition, the SOI platform is not commonly used for electronicchip fabrication, which makes it impossible to monolithically integratehigh performance photonic and electronic circuits together. Even for theelectronic chips based on SOI, the SOI wafer specifications aresignificantly different from those of the silicon photonics wafers.

Special fabrication processes, such as high temperature annealing andepitaxial growth, are typically needed to fabricate fundamental photonicelements, such as modulators and photodetectors, for the SOI-basedsilicon photonics. These high temperature processes may ruin theelectrical properties of the electronic devices, which makes itincompatible with the electronic chip fabrication. The cost of aSOI-based silicon photonic chip is high. A nitride/oxide-based platform,on the other hand, can only be used as passive and low-speedapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that various features are not necessarily drawn to scale. In fact,the dimensions and geometries of the various features may be arbitrarilyincreased or reduced for clarity of illustration.

FIG. 1A illustrates a cross-sectional view of an exemplary photonicdevice, in accordance with some embodiments of present disclosure.

FIG. 1B illustrates another cross-sectional view of the exemplaryphotonic device in FIG. 1A, in accordance with some embodiments ofpresent disclosure.

FIG. 2A illustrates a top view of an exemplary photonic device element,in accordance with some embodiments of present disclosure.

FIG. 2B illustrates a cross-sectional view of the exemplary photonicdevice element in FIG. 2A, in accordance with some embodiments ofpresent disclosure.

FIG. 3A illustrates a top view of another exemplary photonic deviceelement, in accordance with some embodiments of present disclosure.

FIG. 3B illustrates a cross-sectional view of the exemplary photonicdevice element in FIG. 3A, in accordance with some embodiments ofpresent disclosure.

FIGS. 4A-4P illustrate cross-sectional views of an exemplary photonicdevice at various stages of a fabrication process, in accordance withsome embodiments of the present disclosure.

FIG. 5 illustrates an exemplary optical communication system, inaccordance with some embodiments of present disclosure.

FIG. 6 illustrates an exemplary method for forming a photonic device, inaccordance with some embodiments of the present disclosure.

FIG. 7 illustrates an exemplary method for forming a photonic materiallayer in a photonic device, in accordance with some embodiments of thepresent disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following disclosure describes various exemplary embodiments forimplementing different features of the subject matter. Specific examplesof components and arrangements are described below to simplify thepresent disclosure. These are, of course, merely examples and are notintended to be limiting. For example, it will be understood that when anelement is referred to as being “connected to” or “coupled to” anotherelement, it may be directly connected to or coupled to the otherelement, or one or more intervening elements may be present.

To achieve a high speed optical interconnection between photonicelements, the present teaching discloses a photonic device packageincluding: patterned passive routing structures based on alow-temperature deposited material, e.g. silicon nitride, and high speedactive structures, e.g. modulators and photodetectors, based on grapheneor other two-dimensional (2D) photonic materials. The photonic devicepackage is formed based on a bulk silicon wafer process, which leads toa lower cost and makes it possible to be integrated to all thetechnology nodes. A sufficient optical isolation, e.g. larger than 1micrometer separation, is on the top metal routing layers. Because thephotonic materials and elements are deposited or transferred at lowtemperatures, the disclosed process flow is compatible with a standardcomplementary metal oxide semiconductor (CMOS) process.

The disclosed high speed interconnection system and its fabricationprocess are flexible compared to a standard SOI platform, which alwaysstarts with an expensive SOI wafer where all critical elements are onthe SOI layer. In the disclosed system, the photonic layer can beorganic or inorganic, and can be placed anywhere on the verticaldirection (perpendicular to the wafer surface) with an optical isolationfrom the high-index metal layers. The disclosed system monolithicallyintegrates high performance photonic and electronic circuits togetherwithout a need of hybrid bonding or stacking of a photonic chip to anelectronic chip.

Due to the strong opto-electrical tuning coefficients (in terms of bothrefractive index and absorption), the disclosed device and system areultra-compact and power efficient. An optical communication system basedon the disclosed photonic devices can be built without a thermal tuning,which boosts the power efficiency with a broadband response, coveringall the commonly used O-band, C-band, L-band, etc.

FIG. 1A illustrates a cross-sectional view of an exemplary photonicdevice 100, in accordance with some embodiments of present disclosure.It is noted that the photonic device 100 is merely an example, and isnot intended to limit the present disclosure. Accordingly, it isunderstood that additional functional blocks may be provided in orcoupled to the photonic device 100 of FIG. 1A, and that some otherfunctional blocks may only be briefly described herein.

Referring to FIG. 1A, the photonic device 100 comprises: a substrate110; a plurality of metal layers 120 on the substrate 110; a photonicmaterial layer 140 over the plurality of metal layers 120; and anoptical routing layer 150 comprising a waveguide 155 on the photonicmaterial layer 140. In one embodiment, the substrate 110 is made of bulksilicon. As shown in FIG. 1A, the substrate 110 may compriseimplantation regions 111, 112 with dopants. For example, each of theimplantation regions 111 is doped with a p-type material; while each ofthe implantation regions 112 is doped with an n-type material.

As shown in FIG. 1A, the photonic device 100 further comprises anoptical isolation layer 130 on the plurality of metal layers 120. In oneembodiment, the optical isolation layer 130 comprises a relatively thicklow refractive index material, e.g. silicon oxide with a thickness 131of at least one micrometer, to isolate the optical routing in thewaveguide 155 or a wavelength division multiplexing (WDM) of the opticalrouting layer 150 from the leaky lossy materials in the plurality ofmetal layers 120.

As shown in FIG. 1A, the photonic device 100 further comprises aplurality of metal vias 132 extending through the optical isolationlayer 130 and onto the plurality of metal layers 120. As shown in FIG.1A, the photonic device 100 further comprises a contact layer 136comprising a plurality of contacts each of which is formed on and incontact with a corresponding one of the plurality of metal vias 132. Thephotonic material layer 140 is formed on and in contact with the contactlayer 136. In accordance with various embodiments, each of the pluralityof contacts 136 comprises at least one of: nickel, palladium, orchromium.

The waveguide 155 in the optical routing layer 150 may include a passiveoptical routing material, such as silicon nitride, polycrystallinesilicon, etc., which is deposited and patterned to guide a light 101 orelectromagnetic wave 105. In one embodiment, the waveguide 155 and thephotonic material layer 140 form various photonic elements, e.g. amodulator 157 or a photodetector 158. In accordance with variousembodiments, the photonic material layer 140 comprises a plurality ofphotonic material regions 140-1, 140-2 distributed in the photonicelements 157, 158 respectively. In accordance with various embodiments,different photonic material regions 140-1, 140-2 may include same ordifferent sublayers, e.g. at least one graphene sublayer comprisinggraphene, and at least one dielectric sublayer comprising a dielectricmaterial.

In one embodiment, before the patterning of the optical routingstructures in the optical routing layer 150, 2D photonic materials, suchas graphene, are deposited or transferred to the top of the wafer andpatterned in the photonic material layer 140. This material, by properlyelectrical biasing and optical mode overlapping with the light guidingstructure in the optical routing layer 150, can be used to realize highspeed optical signal modulation and detection.

As shown in FIG. 1A, the photonic device 100 further comprises anoptical cladding layer 160 on the optical routing layer 150; and a topmetal routing layer 170 on the optical cladding layer 160. In accordancewith various embodiments, the optical cladding layer 160 comprises arelatively thick low refractive index material, e.g. silicon oxide witha thickness 161 of at least one micrometer, to isolate the opticalrouting in the waveguide 155 or a wavelength division multiplexing (WDM)of the optical routing layer 150 from the leaky lossy materials in thetop metal routing layer 170. In one embodiment, the top metal routinglayer 170 may include or serve as a power distribution layer.

FIG. 1B illustrates another cross-sectional view of the exemplaryphotonic device 100 in FIG. 1A, in accordance with some embodiments ofpresent disclosure. The cross-sectional view of the photonic device 100in FIG. 1A is taken along the B-B′ direction as shown in FIG. 1B. Thecross-sectional view of the photonic device 100 in FIG. 1B is takenalong the A-A′ direction as shown in FIG. 1A. As shown in FIG. 1B, thephotonic device 100 comprises: a substrate 110; a plurality of metallayers 120 on the substrate 110; a photonic material layer 140 over theplurality of metal layers 120; and an optical routing layer 150comprising waveguides 155 on the photonic material layer 140. In oneembodiment, the substrate 110 is made of bulk silicon and comprisesimplantation regions 111, 112 with dopants.

As shown in FIG. 1B, the photonic device 100 comprises a plurality ofmetal vias 132 extending through the optical isolation layer 130 andonto the plurality of metal layers 120. Each of the plurality of metalvias 132 comprises at least one inter-level metal layer 134 over theplurality of metal layers 120, to ease the via process for metallayer-to-layer connection.

As shown in FIG. 1B, the photonic device 100 further comprises aplurality of metal vias 162 extending through the optical cladding layer160, the optical routing layer 150, the photonic material layer 140, andonto contacts 136 in the contact layer. Each of the plurality of metalvias 162 comprises at least one inter-level metal layer 164, to ease thevia process for metal layer-to-layer connection. As shown in FIG. 1B,the photonic device 100 further comprises some contact openings 180 onthe top metal routing layer 170.

As shown in FIG. 1B, the photonic material layer 140 includes aplurality of sublayers, e.g. a first graphene sublayer 141 comprisinggraphene, a first dielectric sublayer 142 comprising a first dielectricmaterial on the first graphene sublayer 141, a second graphene sublayer145 comprising graphene on the first dielectric sublayer 142, and asecond dielectric sublayer 146 comprising a second dielectric materialon the second graphene sublayer 145. Each of the first dielectricmaterial and the second dielectric material may be: aluminum oxide,silicon nitride, or silicon oxide. In one embodiment, the opticalrouting material in the waveguides 155 is the same as the firstdielectric material and the second dielectric material, e.g. siliconnitride.

As shown in FIG. 1B, each of the first graphene sublayer 141 and thesecond graphene sublayer 145 is on and in contact with a contact 136,while the first graphene sublayer 141 and the second graphene sublayer145 are electrically isolated by the first dielectric sublayer 142.Depending on different functions of different electronic elements, thesecond graphene sublayer 145 is distributed in some electronic elementsbut not others.

In the example shown in FIG. 1B, the photonic material layer 140comprises graphene located below a bottom surface of at least one of theplurality of waveguides 155. In other embodiments of the presentteaching, the photonic material layer 140 comprises graphene locatedwithin, e.g. at a center of, at least one of the plurality ofwaveguides.

FIG. 2A illustrates a top view of an exemplary photonic device element200, in accordance with some embodiments of present disclosure. In oneembodiment, the photonic device element 200 is a component, e.g. amodulator, in a photonic device 100 as shown in FIG. 1A and FIG. 1B.

As shown in FIG. 2A, the photonic device element 200 comprises awaveguide 255 on top of a photonic material layer comprising graphene245 on two contacts 236-1, 236-2. Each of the two contacts 236-1, 236-2has a band or rectangular shape. The two contacts 236-1, 236-2 arelocated in parallel below the graphene 245.

FIG. 2B illustrates a cross-sectional view of the exemplary photonicdevice element 200 in FIG. 2A, in accordance with some embodiments ofpresent disclosure. The cross-sectional view of the photonic deviceelement 200 in FIG. 2B is taken along the C-C′ direction as shown inFIG. 2A.

As shown in FIG. 2B, the photonic device element 200 comprises awaveguide 255 on top of a photonic material layer 240 on and in contactwith two contacts 236-1, 236-2. Each of the two contacts 236-1, 236-2 islocated on a metal via 232.

As shown in FIG. 2B, the photonic material layer 240 includes twographene sublayers 241, 245, each of which includes graphene on and incontact with a corresponding one of the contacts 236-1, 236-2. Thegraphene sublayer 241 is on and in contact with the contact 236-1. Apart of the graphene sublayer 245 is on and in contact with the contact236-2; while another part of the graphene sublayer 245 is over thegraphene sublayer 241 and separated from the graphene sublayer 241 by adielectric material, e.g. aluminum oxide, silicon nitride, or siliconoxide. In one embodiment, the two graphene sublayers 241, 245 may serveas two electrodes in the modulator 200.

In accordance with various embodiments, each of the two graphenesublayers 241, 245 has a thickness of about 0.3 nanometer, which is athickness of a single carbon atom. In accordance with variousembodiments, the waveguide 255 has a thickness T between 400 nanometersand 800 nanometers, and has a width W between 500 nanometers and 2000nanometers. In accordance with various embodiments, the photonicmaterial layer 240 including the dielectric material has a totalthickness t between 5 nanometers and 100 nanometers.

Referring back to FIG. 2A, the photonic device element 200 may receivean input of a continuous wave light 201, which may be a light with asingle wavelength from a laser. Based on the continuous wave light 201,the photonic device element 200 may convert electrical signals intooptical signals to perform signal modulation; process the opticalsignals; and send the optical signals 205 out via the waveguide 255. Theelectrical signals may come from metal layers below the photonicmaterial layer 240 via the contacts 236-1, 236-2, and the graphenesublayers 241, 245.

FIG. 3A illustrates a top view of another exemplary photonic deviceelement 300, in accordance with some embodiments of present disclosure.In one embodiment, the photonic device element 300 is a component, e.g.a photodetector, in a photonic device 100 as shown in FIG. 1A and FIG.1B.

As shown in FIG. 3A, the photonic device element 300 comprises awaveguide 255 on top of a photonic material layer comprising graphene341 on two contacts 336-1, 336-2. Each of the two contacts 336-1, 336-2has a base portion and multiple finger branches connected to the baseportion. The base portions of the two contacts 336-1, 336-2 are locatedin parallel below the graphene 341. The finger branches of the twocontacts 336-1, 336-2 are interlaced and placed in parallel below thegraphene 341.

FIG. 3B illustrates a cross-sectional view of the exemplary photonicdevice element 300 in FIG. 3A, in accordance with some embodiments ofpresent disclosure. The cross-sectional view of the photonic deviceelement 300 in FIG. 3B is taken along the D-D′ direction as shown inFIG. 3A.

As shown in FIG. 3B, the photonic device element 300 comprises awaveguide 255 on top of a photonic material layer 340 on and in contactwith the two contacts 336-1, 336-2. Each of the two contacts 336-1,336-2 is located on a metal via 332.

As shown in FIG. 3B, the photonic material layer 340 comprises agraphene sublayer 341 including graphene on and in contact with thecontacts 336-1, 336-2. The photonic material layer 340 further comprisesa dielectric material, e.g. aluminum oxide, silicon nitride, or siliconoxide, on the graphene sublayer 341.

In accordance with various embodiments, the graphene sublayer 341 has athickness of about 0.3 nanometer, which is a thickness of a singlecarbon atom. In accordance with various embodiments, the waveguide 255has a thickness T between 400 nanometers and 800 nanometers, and has awidth W between 500 nanometers and 2000 nanometers. In accordance withvarious embodiments, the photonic material layer 340 including thedielectric material has a total thickness t between 5 nanometers and 100nanometers.

In one embodiment, the waveguide 255 in FIG. 2A and FIG. 3A is a samewaveguide. The photonic device element 300 may receive the opticalsignals 205 from the photonic device element 200; process the opticalsignals 205; convert the optical signals 205 into electrical signals;and send the electrical signals down to the metal layers below thephotonic material layer 340 via the graphene sublayer 341 and thecontacts 336-1, 336-2.

In one embodiment, a unified material, e.g. silicon nitride, is used forall the devices used in the photonic interconnect system, includingmodulators, photodetectors, passive routing structures. On device level,the graphene contacts 236-1, 236-2 are put on the bottom surface of themodulator and photodetector to simply the process. In accordance withvarious embodiments, the graphene sublayer is in contact with or putinto the waveguide structure of the modulator and photodetector, whichcan further boost the device performance.

FIGS. 4A-4P illustrate cross-sectional views of an exemplary photonicdevice at various stages of a fabrication process, in accordance withsome embodiments of the present disclosure. FIG. 4A is a cross-sectionalview of the photonic device 400-1 including a substrate 410, at one ofthe various stages of fabrication, according to some embodiments of thepresent disclosure. The substrate 410 may be formed of bulk silicon.

FIG. 4B is a cross-sectional view of the photonic device 400-2 includingimplantation regions 411, 412 with dopants formed in the substrate 410,at one of the various stages of fabrication, according to someembodiments of the present disclosure. For example, each of theimplantation regions 411 is doped with a p-type material; while each ofthe implantation regions 412 is doped with an n-type material. Theimplantation regions 411 may be formed by: defining a first geometricpattern from a photomask to the substrate 410 based on photolithography;and doping, according to the first geometric pattern, a p-type materialinto the substrate 410 to form the implantation regions 411. Theimplantation regions 412 may be formed by: defining a second geometricpattern from a photomask to the substrate 410 based on photolithography;and doping, according to the second geometric pattern, an n-typematerial into the substrate 410 to form the implantation regions 412.

FIG. 4C is a cross-sectional view of the photonic device 400-3 includinga plurality of metal layers 420 on the substrate 410, at one of thevarious stages of fabrication, according to some embodiments of thepresent disclosure. The plurality of metal layers 420 may be formed bydepositing a metal material like copper, aluminum, silver, etc.

FIG. 4D is a cross-sectional view of the photonic device 400-4 includingan optical isolation layer 430 and a plurality of metal vias 432 formedin the optical isolation layer 430, at one of the various stages offabrication, according to some embodiments of the present disclosure.The optical isolation layer 430 may be formed by depositing an opticalisolation material with a thickness of at least one micrometer on theplurality of metal layers 420. In various embodiments, different lowrefractive index materials can be used as the optical isolationmaterial, where one example is silicon oxide. The plurality of metalvias 432 may be formed by: etching the optical isolation layer 430 toform etched regions with a pattern; depositing a metal material,according to the pattern, into the etched regions to form the pluralityof metal vias 432 extending through the optical isolation layer 430 andonto the plurality of metal layers 420. Each of the plurality of metalvias 432 may be formed by multiple sub-stages, with an inter-level metallayer 434 formed between two adjacent sub-stages.

FIG. 4E is a cross-sectional view of the photonic device 400-5 includinga contact layer comprising a plurality of metal contacts 436 formed inthe optical isolation layer 430, at one of the various stages offabrication, according to some embodiments of the present disclosure.Each of the plurality of metal contacts 436 may be formed by: defining apattern based on the plurality of metal vias; depositing, according tothe pattern, a metal material on and in contact with a corresponding oneof the plurality of metal vias 432; and polishing the contacts with achemical mechanical polishing (CMP) process. In one embodiment, aDamascene process may be used to form the contact layer with a flat topsurface. In accordance with various embodiments, to reduce contactresistance, a metal different from the conventional copper, such asnickel, palladium, chromium, or metal alloy, can be used. While FIG. 4Eshows one possible process to make contact with graphene, an alternativeway to make contact with graphene is to deposit graphene first, thenpattern the contact by a lift-off process.

FIG. 4F is a cross-sectional view of the photonic device 400-6, where afirst photonic material sublayer 441 is formed on the contact layer 436,at one of the various stages of fabrication, according to someembodiments of the present disclosure. This may be performed bydepositing a first two-dimensional material, e.g. graphene, onto thecontact layer 436 according to a first pattern to form the firstphotonic material sublayer 441. In various embodiments, the singleatomic graphene sublayer 441 can be formed by: either a chemical vapordeposition (CVD) process or a transfer from a graphene coated copperfoil at wafer or chip level. A low temperature rapid thermal annealingcan be used to reduce the contact resistance to the graphene. Forexample, the first photonic material sublayer 441 may be annealed at atemperature between 200 degrees Celsius and 300 degrees Celsius.

FIG. 4G is a cross-sectional view of the photonic device 400-7, where afirst dielectric sublayer 442 is formed on the first photonic materialsublayer 441, at one of the various stages of fabrication, according tosome embodiments of the present disclosure. This may be performed by:depositing a first dielectric material onto the first photonic materialsublayer 441 to form the first dielectric sublayer 442; and etching thefirst dielectric sublayer 442 to form a second pattern. The thindielectric sublayer 442 is deposited to protect the graphene 441 and/orto insulate two graphene sublayers for a high-speed modulator. The firstdielectric material may comprise at least one of: aluminum oxide,silicon nitride, or silicon oxide. According to the second pattern, thefirst dielectric sublayer 442 has two portions 442-1, 442-2 separated bya trench 443 on and exposing one of the contacts 436.

FIG. 4H is a cross-sectional view of the photonic device 400-8, where asecond photonic material sublayer 445 is formed on the first dielectricsublayer 442, at one of the various stages of fabrication, according tosome embodiments of the present disclosure. This may be performed bydepositing a second two-dimensional material, e.g. graphene, onto thefirst dielectric sublayer 442 according to the second pattern to formthe second photonic material sublayer 445. To be specific, the secondtwo-dimensional material is deposited partially onto the dielectricportion 442-1, and deposited into the trench 443 and onto the exposedcontact 436. In various embodiments, the single atomic graphene sublayer445 can be formed by: either a chemical vapor deposition (CVD) processor a transfer from a graphene coated copper foil at wafer or chip level.A low temperature rapid thermal annealing can be used to reduce thecontact resistance to the graphene. For example, the second photonicmaterial sublayer 445 may be annealed at a temperature between 200degrees Celsius and 300 degrees Celsius.

FIG. 4I is a cross-sectional view of the photonic device 400-9, where asecond dielectric sublayer 446 is formed on the second photonic materialsublayer 445, at one of the various stages of fabrication, according tosome embodiments of the present disclosure. This may be performed by:depositing a second dielectric material onto the second photonicmaterial sublayer 445 and the first dielectric sublayer 442 to form thesecond dielectric sublayer 446. The second dielectric material maycomprise at least one of: aluminum oxide, silicon nitride, or siliconoxide. As such, a photonic material layer 440 is formed to comprise: thefirst photonic material sublayer 441, the first dielectric sublayer 442,the second photonic material sublayer 445, and the second dielectricsublayer 446. After this stage, the graphene sublayers 441, 445 andtheir contacts 436 are sealed by the dielectric material.

FIG. 4J is a cross-sectional view of the photonic device 400-10, wherean optical routing layer 450 is deposited onto the second dielectricsublayer 446, at one of the various stages of fabrication, according tosome embodiments of the present disclosure. This may be performed by:depositing silicon oxide onto the second dielectric sublayer 446, andpolishing the silicon oxide based on a chemical mechanical polishing orplanarization process.

FIG. 4K is a cross-sectional view of the photonic device 400-11, where aplurality of etched regions 452 is formed in the optical routing layer450, at one of the various stages of fabrication, according to someembodiments of the present disclosure. This may be performed by:defining a geometric pattern from a photomask to the optical routinglayer 450 based on photolithography; and etching the silicon oxide inthe optical routing layer 450 to form etched regions 452 with astructure pattern.

FIG. 4L is a cross-sectional view of the photonic device 400-12, where aplurality of waveguides 455 is formed in the etched regions 452, at oneof the various stages of fabrication, according to some embodiments ofthe present disclosure. This may be performed by: depositing, accordingto the structure pattern, an optical routing material into the etchedregions 452 and onto the photonic material layer 440; and polishing theoptical routing material to form the optical routing layer 450comprising a plurality of waveguides 455. The optical routing materialmay comprise at least one of: silicon (Si) nitride, aluminum oxide,polycrystalline-Si, amorphous-Si, Si-rich silicon oxide, or an organicmaterial like SU8. In one embodiment, a same material is used in theplurality of waveguides 455, the first dielectric sublayer 442, and thesecond dielectric sublayer 446. After this stage, optical routingstructures are formed in the optical routing layer 450 to transferoptical signals inside the chip or to the chip edge for an inter-chipcommunication. In one embodiment, the stages in FIG. 4J to FIG. 4L canbe performed based on a Damascene process to pattern the optical routingstructures.

FIG. 4M is a cross-sectional view of the photonic device 400-13, wherean optical cladding layer 460 is formed on the optical routing layer450, at one of the various stages of fabrication, according to someembodiments of the present disclosure. This may be performed by:depositing silicon oxide with a thickness of at least one micrometer onthe optical routing layer 450 to form the optical cladding layer 460.

FIG. 4N is a cross-sectional view of the photonic device 400-14, where aplurality of metal vias 462 is formed through the optical cladding layer460, at one of the various stages of fabrication, according to someembodiments of the present disclosure. This may be performed by:depositing silicon oxide with a thickness of at least one micrometer onthe optical routing layer 450 to form the optical cladding layer 460.The plurality of metal vias 462 may be formed by: defining a geometricpattern from a photomask to the optical cladding layer 460 based onphotolithography; etching the optical cladding layer 460, the opticalrouting layer 450, and the photonic material layer 440 to form etchedregions with a pattern; depositing a metal material, according to thepattern, into the etched regions to form the plurality of metal vias 462extending through the optical cladding layer 460, the optical routinglayer 450, and the photonic material layer 440 and onto some of thecontacts 436. Each of the plurality of metal vias 462 may be formed bymultiple sub-stages, with an inter-level metal layer 464 formed betweentwo adjacent sub-stages.

FIG. 4O is a cross-sectional view of the photonic device 400-15, where atop metal routing layer 470 is formed on the optical cladding layer 460,at one of the various stages of fabrication, according to someembodiments of the present disclosure. The top metal routing layer 470may be formed by depositing a metal material like copper, aluminum,silver, etc., onto the optical cladding layer 460, with a polishingprocess. With the optical cladding layer 460 being thick enough toisolate the optical routing in the plurality of waveguides 455, metalroutings, such as power distribution layers, can be patterned in the topmetal routing layer 470. As such, the optical cladding layer 460 alsoserves as an optical isolation layer between the optical routing layer450 and the top metal routing layer 470.

FIG. 4P is a cross-sectional view of the photonic device 400-16, wherecontact openings 480 are formed on the top metal routing layer 470, atone of the various stages of fabrication, according to some embodimentsof the present disclosure. The contact openings 480 may be formed basedon a deposition process, an etching process, and a clean process.

FIG. 5 illustrates an exemplary optical communication system 500, inaccordance with some embodiments of present disclosure. As shown in FIG.5 , the optical communication system 500 includes: an electrical tooptical convertor 520 and an optical to electrical convertor 560. Invarious embodiments, each of the electrical to optical convertor 520 andthe optical to electrical convertor 560 may have a structure similar tothat shown in FIGS. 1-4 . For example, each of the electrical to opticalconvertor 520 and the optical to electrical convertor 560 may comprise:a bulk silicon substrate, a plurality of metal layers on the bulksilicon substrate, a plurality of waveguides over the plurality of metallayers, and a photonic material layer comprising graphene located belowa top surface of each of the plurality of waveguides. In one embodiment,the photonic material layer comprises graphene located below a bottomsurface of at least one of the plurality of waveguides. In anotherembodiment, the photonic material layer comprises graphene locatedwithin, e.g. at a center of, at least one of the plurality ofwaveguides. The optical communication system 500 may include high speeddevices based on graphene, which may be deposited or transferred onwafer level or die level.

As shown in FIG. 5 , the electrical to optical convertor 520 isconfigured for converting electrical signals into optical signals, basedon a continuous wave light input 510, where the plurality of waveguides531, 532 in the electrical to optical convertor 520 forms first Nchannels 521, 522 for transmitting optical signals. Similarly, theplurality of waveguides 551, 552 in the optical to electrical convertor560 forms second N channels 561, 562 for transmitting optical signals.The optical to electrical convertor 560 is configured for convertingoptical signals into electrical signals.

As shown in FIG. 5 , the optical communication system 500 furtherincludes: an optical coupler 540 coupled between the electrical tooptical convertor 520 and the optical to electrical convertor 560; asignal multiplexer 530 coupled between the electrical to opticalconvertor 520 and the optical coupler 540; and a signal de-multiplexer550 coupled between the optical coupler 540 and the optical toelectrical convertor 560. The optical coupler 540 may be an edge coupleror a grating coupler configured to realize an inter-chip opticalcommunication.

The signal multiplexer 530 is configured for multiplexing the first Nchannels 531, 532 into a single channel. The signal de-multiplexer 550is configured for de-multiplexing the single channel into the second Nchannels 551, 552. In various embodiments, different optical signalmultiplexing (and de-multiplexing) schemes can be used, e.g. wavelengthmultiplexing, space multiplexing, mode multiplexing, etc. to furtherboost the information stream density.

FIG. 6 illustrates an exemplary method 600 for forming a photonicdevice, in accordance with some embodiments of the present disclosure.The method 600 begins at operation 602, where a plurality of metallayers is formed on a bull(silicon substrate. At operation 604, anoptical isolation layer is deposited on the plurality of metal layers.At operation 606, the optical isolation layer is etched to form apattern. According to the pattern, metal vias extending through theoptical isolation layer are formed at operation 608 onto the metallayers. According to the pattern, a contact layer is deposited atoperation 610, wherein the contact layer comprises metal contacts eachof which is deposited on a corresponding one of the metal vias. Atoperation 612, a photonic material layer comprising at least onetwo-dimensional (2D) material is formed on the contact layer.

At operation 614, silicon oxide is deposited onto the photonic materiallayer. At operation 616, the silicon oxide is etched to form a structurepattern. According to the structure pattern, an optical routing materialis deposited at operation 618 onto the photonic material layer. Atoperation 620, the optical routing material is polished to form anoptical routing layer comprising a plurality of waveguides. At operation622, an optical cladding layer is deposited on the optical routinglayer. At operation 624, a top metal routing layer is formed on theoptical cladding layer. The order of the operations shown in FIG. 6 maybe changed according to different embodiments of the present disclosure.

FIG. 7 illustrates an exemplary method 700 for forming a photonicmaterial layer in a photonic device, in accordance with some embodimentsof the present disclosure. In one embodiment, the method 700 may be usedto perform the operation 612 in the method 600 shown in FIG. 6 .

The method 700 begins at operation 702, where a first pattern isdetermined. At operation 704, a first two-dimensional material, e.g.graphene, is deposited or transferred onto the contact layer accordingto the first pattern to form a first photonic material sublayer. Atoperation 706, the first photonic material sublayer is annealed at atemperature between 200° C. and 300° C. At operation 708, a firstdielectric material is deposited onto the first photonic materialsublayer to form a first dielectric sublayer.

At operation 710, where the first dielectric sublayer is etched to forma second pattern. At operation 712, a second two-dimensional material,e.g. graphene, is deposited or transferred onto the first dielectricsublayer according to the second pattern to form a second photonicmaterial sublayer. At operation 714, the second photonic materialsublayer is annealed at a temperature between 200° C. and 300° C. Atoperation 716, a second dielectric material is deposited onto the secondphotonic material sublayer and partially onto the first dielectricsublayer to form a second dielectric sublayer. The order of theoperations shown in FIG. 7 may be changed according to differentembodiments of the present disclosure.

In one embodiment, a photonic device is disclosed. The photonic deviceincludes: a substrate; a plurality of metal layers on the substrate; aphotonic material layer comprising graphene over the plurality of metallayers; and an optical routing layer comprising a waveguide on thephotonic material layer.

In another embodiment, an optical communication system is disclosed. Theoptical communication system includes: an electrical to opticalconvertor; and an optical to electrical convertor. Each of theelectrical to optical convertor and the optical to electrical convertorcomprises: a bulk silicon substrate, a plurality of metal layers on thebulk silicon substrate, a plurality of waveguides over the plurality ofmetal layers, and a photonic material layer comprising graphene locatedbelow a top surface of each of the plurality of waveguides.

In yet another embodiment, a method for forming a photonic device isdisclosed. The method includes: forming a plurality of metal layers on abulk silicon substrate; depositing a contact layer comprising aplurality of metal contacts over the plurality of metal layers; forminga photonic material layer comprising at least one two-dimensionalmaterial on the contact layer; and depositing, according to a structurepattern, an optical routing material onto the photonic material layer toform an optical routing layer comprising a plurality of waveguides.

The foregoing outlines features of several embodiments so that thoseordinary skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A photonic device, comprising: a substrate; aplurality of metal layers on the substrate; a contact layer comprising aplurality of contacts over the plurality of metal layers; a photonicmaterial layer disposed on the contact layer; and a waveguide on thephotonic material layer, wherein the photonic material layer comprises:a first photonic material sublayer, a first dielectric sublayer, asecond photonic material sublayer, and a second dielectric sublayer, andeach of the first photonic material sublayer and the second photonicmaterial sublayer is formed on and in contact with the contact layer. 2.The photonic device of claim 1, wherein: the substrate is made of bulksilicon.
 3. The photonic device of claim 1, further comprising: anoptical isolation layer on the plurality of metal layers.
 4. Thephotonic device of claim 3, wherein the optical isolation layercomprises silicon oxide with a thickness of at least one micrometer. 5.The photonic device of claim 3, further comprising: a plurality of metalvias extending through the optical isolation layer and onto theplurality of metal layers, wherein each of the plurality of metal viascomprises at least one inter-level metal layer over the plurality ofmetal layers.
 6. The photonic device of claim 5, wherein each of theplurality of contacts is formed on and in contact with a correspondingone of the plurality of metal vias.
 7. The photonic device of claim 6,wherein each of the plurality of contacts comprises at least one of:nickel, palladium, or chromium.
 8. The photonic device of claim 6,wherein the photonic material layer comprises: at least one graphenesublayer comprising graphene; and at least one dielectric sublayercomprising a dielectric material.
 9. The photonic device of claim 6,wherein the waveguide and the photonic material layer form at least oneof: a modulator or a photodetector.
 10. The photonic device of claim 1,further comprising: an optical routing layer; an optical cladding layeron the optical routing layer, wherein the optical cladding layercomprises silicon oxide with a thickness of at least one micrometer; anda top metal routing layer on the optical cladding layer.
 11. An opticalcommunication system, comprising: an electrical to optical convertor;and an optical to electrical convertor, wherein each of the electricalto optical convertor and the optical to electrical convertor comprises:a substrate, a plurality of metal layers on the substrate, a contactlayer comprising a plurality of contacts over the plurality of metallayers, a plurality of waveguides over the contact layer, and a photonicmaterial layer located below a top surface of each of the plurality ofwaveguides, wherein the photonic material layer comprises: a firstphotonic material sublayer, and a second photonic material sublayer, andeach of the first photonic material sublayer and the second photonicmaterial sublayer is formed on and in contact with the contact layer.12. The optical communication system of claim 11, wherein: theelectrical to optical convertor is configured for converting electricalsignals into optical signals, based on a continuous wave light input;the plurality of waveguides in the electrical to optical convertor formsfirst N channels for transmitting optical signals; the plurality ofwaveguides in the optical to electrical convertor forms second Nchannels for transmitting optical signals; and the optical to electricalconvertor is configured for converting optical signals into electricalsignals.
 13. The optical communication system of claim 12, furthercomprising: an optical coupler that is coupled between the electrical tooptical convertor and the optical to electrical convertor and isconfigured for an inter-chip optical communication; a signal multiplexerthat is coupled between the electrical to optical convertor and theoptical coupler, and configured for multiplexing the first N channelsinto a single channel; and a signal de-multiplexer that is coupledbetween the optical coupler and the optical to electrical convertor, andconfigured for de-multiplexing the single channel into the second Nchannels.
 14. The optical communication system of claim 11, wherein: thephotonic material layer comprises graphene located below a bottomsurface of at least one of the plurality of waveguides.
 15. The opticalcommunication system of claim 11, wherein: the photonic material layercomprises graphene located at a center of at least one of the pluralityof waveguides.
 16. A method for forming a photonic device, comprising:forming a plurality of metal layers on a substrate; depositing a contactlayer comprising a plurality of metal contacts over the plurality ofmetal layers; forming a photonic material layer comprising at least onetwo-dimensional material on the contact layer, wherein the photonicmaterial layer comprises: a first photonic material sublayer, a firstdielectric sublayer, a second photonic material sublayer, and a seconddielectric sublayer, each of the first photonic material sublayer andthe second photonic material sublayer is formed on and in contact withthe contact layer; and forming an optical routing layer on the photonicmaterial layer, the optical routing layer comprising a plurality ofwaveguides.
 17. The method of claim 16, further comprising: depositingan optical isolation layer on the plurality of metal layers, wherein theoptical isolation layer comprises silicon oxide with a thickness of atleast one micrometer; etching the optical isolation layer to form apattern; and forming a plurality of metal vias extending through theoptical isolation layer and onto the plurality of metal layers, whereineach of the plurality of metal vias comprises at least one inter-levelmetal layer over the plurality of metal layers, wherein: each of theplurality of metal contacts is deposited on and in contact with acorresponding one of the plurality of metal vias.
 18. The method ofclaim 16, wherein forming the photonic material layer comprises:depositing a first two-dimensional material onto the contact layeraccording to a first pattern to form the first photonic materialsublayer; annealing the first photonic material sublayer at atemperature between 200 degrees Celsius and 300 degrees Celsius;depositing a first dielectric material onto the first photonic materialsublayer to form the first dielectric sublayer; etching the firstdielectric sublayer to foil a second pattern; depositing a secondtwo-dimensional material onto the first dielectric sublayer according tothe second pattern to form the second photonic material sublayer;annealing the second photonic material sublayer at a temperature between200 degrees Celsius and 300 degrees Celsius; depositing a seconddielectric material onto the second photonic material sublayer and thefirst dielectric sublayer to form the second dielectric sublayer. 19.The method of claim 18, further comprising: depositing silicon oxideonto the second dielectric sublayer; etching the silicon oxide to formthe structure pattern according to which the optical routing material isdeposited onto the second dielectric sublayer, wherein: the opticalrouting material comprises at least one of: silicon (Si) nitride,aluminum oxide, polycrystalline-Si, amorphous-Si, Si-rich silicon oxide,or an organic material, and the optical routing material is same as thefirst dielectric material and the second dielectric material.
 20. Themethod of claim 16, further comprising: depositing an optical claddinglayer on the optical routing layer, wherein the optical cladding layercomprises silicon oxide with a thickness of at least one micrometer; andforming a top metal routing layer on the optical cladding layer.